11359 10.1140/epjc/s10052-023-11359-4 924 41 Spin density matrix elements in exclusive ρ 0 meson muoproduction Regular Article - Experimental Physics 1 25 2023 2 27 2022 11 4 2023 2 24 2023 10 13 2024 4 12 In the original version of this article, the given and family names of M. Finger jr. were incorrectly structured. ’Finger’ was mistakenly published as the given name, while ’jr.’ was incorrectly indicated as the family name. In the HTML version of this article, the Compass Collaboration was not indicated as the sole author. The article has been corrected. The Author(s) 2023 corrected publication 2024 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/ . Funded by SCOAP3. SCOAP3 supports the goals of the International Year of Basic Sciences for Sustainable Development. 10052 83 83 10 10 COMPASS Collaboration Bakur.Parsamyan@cern.ch Fulvio.Tessarotto@cern.ch Andrzej.Sandacz@ncbj.gov.pl G. D. Alexeev M. G. Alexeev C. Alice A. Amoroso V. Andrieux V. Anosov K. Augsten W. Augustyniak C. D. R. Azevedo B. Badelek J. Barth R. Beck Y. Bedfer J. Bernhard M. Bodlak F. Bradamante A. Bressan V. E. Burtsev W.-C. Chang C. Chatterjee M. Chiosso A. G. Chumakov S.-U. Chung A. Cicuttin P. M. M. Correia M. L. Crespo D. D’Ago S. Dalla Torre S. S. Dasgupta S. Dasgupta F. Del Carro I. Denisenko O. Yu. Denisov S. V. Donskov N. Doshita Ch. Dreisbach W. Dünnweber R. R. Dusaev D. Ecker A. Efremov D. Eremeev P. Faccioli M. Faessler M. Finger M. Finger Jr. H. Fischer K. J. Flöthner W. Florian J. M. Friedrich V. Frolov L.G. Garcia Ordòñez F. Gautheron O. P. Gavrichtchouk S. Gerassimov J. Giarra D. Giordano M. Gorzellik A. Grasso A. Gridin M. Grosse Perdekamp B. Grube M. Grüner A. Guskov D. von Harrach M. Hoffmann N. Horikawa N. d’Hose C.-Y. Hsieh S. Huber S. Ishimoto A. Ivanov T. Iwata M. Jandek V. Jary R. Joosten E. Kabuß F. Kaspar A. Kerbizi B. Ketzer A. Khatun G. V. Khaustov F. Klein J. H. Koivuniemi V. N. Kolosov K. Kondo Horikawa I. Konorov V. F. Konstantinov A. M. Korzenev A. M. Kotzinian O. M. Kouznetsov A. Koval Z. Kral F. Krinner F. Kunne K. Kurek R. P. Kurjata A. Kveton K. Lavickova S. Levorato Y.-S. Lian J. Lichtenstadt P.-J. Lin R. Longo V. E. Lyubovitskij A. Maggiora A. Magnon N. Makins N. Makke G. K. Mallot A. Maltsev S. A. Mamon A. Martin J. Marzec J. Matoušek T. Matsuda G. Mattson C. Menezes Pires F. Metzger M. Meyer W. Meyer Yu. V. Mikhailov M. Mikhasenko E. Mitrofanov D. Miura Y. Miyachi R. Molina A. Moretti A. Nagaytsev C. Naim D. Neyret M. Niemiec J. Nový W.-D. Nowak G. Nukazuka A. G. Olshevsky M. Ostrick D. Panzieri B. Parsamyan Bakur.Parsamyan@cern.ch S. Paul H. Pekeler J.-C. Peng M. Pešek D. V. Peshekhonov M. Pešková S. Platchkov J. Pochodzalla V. A. Polyakov M. Quaresma C. Quintans G. Reicherz C. Riedl D. I. Ryabchikov A. Rychter A. Ryva V. D. Samoylenko A. Sandacz Andrzej.Sandacz@ncbj.gov.pl S. Sarkar I. A. Savin G. Sbrizzai H. Schmieden A. Selyunin K. Sharko L. Sinha M. Slunecka D. Spülbeck A. Srnka M. Stolarski O. Subrt M. Sulc H. Suzuki S. Tessaro F. Tessarotto Fulvio.Tessarotto@cern.ch A. Thiel J. Tomsa F. Tosello A. Townsend T. Triloki V. Tskhay B. Valinoti B. M. Veit J. F. C. A. Veloso B. Ventura M. Virius M. Wagner S. Wallner K. Zaremba M. Zavertyaev M. Zemko E. Zemlyanichkina M. Ziembicki grid.48507.3e 0000 0004 0482 7128 A.I. Alikhanyan National Science Laboratory 2 Alikhanyan Br. Street 0036 Yerevan Armenia grid.438850.2 0000 0004 0428 7459 Institute of Scientific Instruments of the CAS 61264 Brno Czech Republic https://ror.org/02jtk7k02 grid.6912.c 0000 0001 1015 1740 Technical University in Liberec 46117 Liberec Czech Republic https://ror.org/03kqpb082 grid.6652.7 0000 0001 2173 8213 Czech Technical University in Prague 16636 Prague Czech Republic https://ror.org/024d6js02 grid.4491.8 0000 0004 1937 116X Faculty of Mathematics and Physics Charles University 12116 Prague Czech Republic https://ror.org/03xjwb503 grid.460789.4 0000 0004 4910 6535 IRFU, CEA Université Paris-Saclay 91191 Gif-sur-Yvette France grid.5570.7 0000 0004 0490 981X Universität Bochum Institut für Experimentalphysik 44780 Bochum Germany grid.10388.32 0000 0001 2240 3300 Universität Bonn Helmholtz-Institut für Strahlen- und Kernphysik 53115 Bonn Germany grid.10388.32 0000 0001 2240 3300 Universität Bonn Physikalisches Institut 53115 Bonn Germany grid.5963.9 Universität Freiburg Physikalisches Institut 79104 Freiburg Germany grid.5802.f 0000 0001 1941 7111 Universität Mainz Institut für Kernphysik 55099 Mainz Germany https://ror.org/02kkvpp62 grid.6936.a 0000 0001 2322 2966 Technische Universität München Physik Department 85748 Garching Germany https://ror.org/05591te55 grid.5252.0 0000 0004 1936 973X Ludwig-Maximilians-Universität 80539 München Germany Matrivani Institute of Experimental Research & Education Calcutta 700 030 India https://ror.org/04mhzgx49 grid.12136.37 0000 0004 1937 0546 School of Physics and Astronomy Tel Aviv University 69978 Tel Aviv Israel grid.419330.c 0000 0001 2184 9917 Abdus Salam ICTP 34151 Trieste Italy grid.470223.0 0000 0004 1760 7175 Trieste Section of INFN 34127 Trieste Italy https://ror.org/02n742c10 grid.5133.4 0000 0001 1941 4308 Dept. of Physics University of Trieste 34127 Trieste Italy grid.470222.1 0000 0004 7471 9712 Torino Section of INFN 10125 Torino Italy https://ror.org/048tbm396 grid.7605.4 0000 0001 2336 6580 Dept. of Physics University of Torino 10125 Torino Italy https://ror.org/0447kww10 grid.410849.0 0000 0001 0657 3887 University of Miyazaki Miyazaki 889-2192 Japan https://ror.org/04chrp450 grid.27476.30 0000 0001 0943 978X Nagoya University 464 Nagoya Japan https://ror.org/00xy44n04 grid.268394.2 0000 0001 0674 7277 Yamagata University Yamagata 992-8510 Japan https://ror.org/00nzsxq20 grid.450295.f 0000 0001 0941 0848 National Centre for Nuclear Research 02-093 Warsaw Poland https://ror.org/00y0xnp53 grid.1035.7 0000 0000 9921 4842 Warsaw University of Technology Institute of Radioelectronics 00-665 Warsaw Poland https://ror.org/039bjqg32 grid.12847.38 0000 0004 1937 1290 Faculty of Physics University of Warsaw 02-093 Warsaw Poland https://ror.org/00nt41z93 grid.7311.4 0000 0001 2323 6065 Dept. of Physics University of Aveiro, I3N 3810-193 Aveiro Portugal https://ror.org/01hys1667 grid.420929.4 LIP 1649-003 Lisbon Portugal grid.9132.9 0000 0001 2156 142X international laboratory covered by a cooperation agreement with CERN Geneva Switzerland grid.9132.9 0000 0001 2156 142X institute covered by a cooperation agreement with CERN Geneva Switzerland grid.9132.9 0000 0001 2156 142X CERN 1211 Geneva 23 Switzerland grid.28665.3f 0000 0001 2287 1366 Academia Sinica Institute of Physics Taipei 11529 Taiwan https://ror.org/047426m28 grid.35403.31 0000 0004 1936 9991 University of Illinois at Urbana-Champaign Dept. of Physics Urbana IL 61801-3080 USA grid.9132.9 0000 0001 2156 142X CERN 1211 Geneva 23 Switzerland grid.5252.0 0000 0004 1936 973X Retired from Ludwig-Maximilians-Universität 80539 München Germany Abstract We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard exclusive ρ 0 meson muoproduction at COMPASS using 160 GeV/c polarised μ + and μ - beams impinging on a liquid hydrogen target. The measurement covers the kinematic range 5.0 GeV/ c 2 < W < 17.0 GeV/ c 2 , 1.0 (GeV/c) 2 < Q 2 < 10.0 (GeV/c) 2 and 0.01 (GeV/c) 2 < p T 2 < 0.5 (GeV/c) 2 . Here, W denotes the mass of the final hadronic system, Q 2 the virtuality of the exchanged photon, and p T the transverse momentum of the ρ 0 meson with respect to the virtual-photon direction. The measured non-zero SDMEs for the transitions of transversely polarised virtual photons to longitudinally polarised vector mesons ( γ T ∗ → V L ) indicate a violation of s-channel helicity conservation. Additionally, we observe a dominant contribution of natural-parity-exchange transitions and a very small contribution of unnatural-parity-exchange transitions, which is compatible with zero within experimental uncertainties. The results provide important input for modelling Generalised Parton Distributions (GPDs). In particular, they may allow one to evaluate in a model-dependent way the role of parton helicity-flip GPDs in exclusive ρ 0 production. A. Efremov, F. Konstantinov, A. Magnon, V. Mikhailov: Deceased.